text: #ifndef __LINUX_UIO_H
  #define __LINUX_UIO_H
  
  #include <linux/compiler.h>
  #include <linux/types.h>
  
  /*
   *	Berkeley style UIO structures	-	Alan Cox 1994.
   *
   *		This program is free software; you can redistribute it and/or
   *		modify it under the terms of the GNU General Public License
   *		as published by the Free Software Foundation; either version
   *		2 of the License, or (at your option) any later version.
   */
  
  struct iovec
  {
  	void __user *iov_base;	/* BSD uses caddr_t (1003.1g requires void *) */
  	__kernel_size_t iov_len; /* Must be size_t (1003.1g) */
  };
  
  #ifdef __KERNEL__
  
  struct kvec {
  	void *iov_base; /* and that should *never* hold a userland pointer */
  	size_t iov_len;
  };
  
  #endif
  
  /*
   *	UIO_MAXIOV shall be at least 16 1003.1g (5.4.1.1)
   */
   
  #define UIO_FASTIOV	8
  #define UIO_MAXIOV	1024
  
  /*
   * Total number of bytes covered by an iovec.
   *
   * NOTE that it is not safe to use this function until all the iovec's
   * segment lengths have been validated.  Because the individual lengths can
   * overflow a size_t when added together.
   */
  static inline size_t iov_length(const struct iovec *iov, unsigned long nr_segs)
  {
  	unsigned long seg;
  	size_t ret = 0;
  
  	for (seg = 0; seg < nr_segs; seg++)
  		ret += iov[seg].iov_len;
  	return ret;
  }
  
  unsigned long iov_shorten(struct iovec *iov, unsigned long nr_segs, size_t to);
  
  #endif
  